Air bearings permit contactless bearing or seating arrangements so that there is no wear and no significant bearing friction. In view of their characteristics, air bearings are advantageously used on the slide guides of measuring slides or carriages in coordinate measuring machines. The accuracy of the measuring slide movement and positioning depends on the height of the air gap between the bearing surface of the bearing body and the mating bearing surface of the slide guide. As far as possible, the height of the air gap must be kept constant. The constancy of the air gap height depends on the accurate regulation of the air supply pressure and the precision of the bearing surface finishes.
When using conventional air bearings, accurate guiding of a measuring slide requires that the measuring slide be mounted by air bearings receiving the slide guide in the direction of gravity, and by additional air bearings facing the slide in a direction opposite to gravity. In this manner, the measuring slide can be accurately guided by the cooperation of a plurality of bearings arranged in different loading directions.
To maintain an ideal state of equilibrium for the measuring slide, the quantity of air to each individual bearing must be controlled. The higher the air pressure used, the more stable or rigid the bearing. Without the cooperation of a large number of air bearings working in opposition, conventional air bearings provide an excessively imprecise or non-fixed working position due to an imprecise air gap height and position for the object to be set.
The working position of conventional air bearings can be displaced by minor imprecisions in the bearing surfaces. This occurs as a result of the air accumulating or stagnating due to the relative displacement movements between the bearing bodies and the mating surface of the slide guide when moving the measuring slide. This air accumulation causes tilting of the bearing resulting from a displacement of the central pressure point of the bearing.